Increasing environmental awareness has led to demands to avoid wasting energy in industrial installations and also, in particular, to use electrical energy efficiently. The “energy management” necessary for this purpose requires as its input variable the detailed monitoring of how energy is distributed within the installation. The flows of energy to the individual loads are of particular interest in this case. Energy is usually fed to the individual loads over a single lead (one phase) or three leads (three phases) depending on whether the load is a single-phase or three-phase one.
Three-phase motors are the principal energy converters in machine installations having turning parts. Said three-phase motors are supplied with energy via control and protective gear usually over spur lines. The three-phase motor connected to the control and protective gear is moreover controlled and monitored by it. The term used for the combination of control and protective gear is “load feeder”. Fuseless load feeders are for example device combinations consisting of a contactor for operational switching and a power circuit-breaker for overload and short-circuit protection.
A three-phase motor is usually supplied with electrical energy over three leads (phases). The leads (phases) are routed to the installation via the load feeder so that the desired control and monitoring of the installation can be performed by the load feeder.
In particular the following factors are of significance for optimizing the consumption values of an installation (e.g. a three-phase motor):                transparent measuring of the energy distribution (effective power, apparent power, reactive power) in the installation,        providing information about the respective load status of the individual load feeders,        initiating control measures (on a central/decentralized basis) for optimizing load feeder efficiency so that the energy efficiency of the installation will be increased.        
Where the control measures are concerned a distinction must be made between (as a rule time-critical, decentralized) efficiency-optimizing closed-loop control processes in the individual feeder (torque control, for example) and energy management control processes conducted centrally by a higher-level control system, for example disconnecting and connecting individual load feeders as a function of the capacity utilization level.
However, fast acquisition of the respective load status in the individual load feeders is the foremost prerequisite for effective energy management.
The phase angle between current and voltage (Cos Phi/cos φ) has proved to be the best characteristic variable for the load status of a motor-driven load feeder. However, since said characteristic variable does not produce clear results across all operating ranges of a motor the respectively associated operating current must be additionally assessed at the same time.
Load feeders are furthermore expected to check the operating condition of the connected installation (condition monitoring) by monitoring how the electric characteristic variables change over time. A distinction has to be made here between long-term changes in behavior (due to wear and tear, for example) and short-term changes in behavior (for example dry-running of pumps, fan belt disengagement in transmission systems, airflow blocking in ventilators). Long-term changes in behavior can be detected using trend analyses (of current consumption, for example). The detection of short-term changes in behavior by contrast requires fast evaluation of measured values. Monitoring the cos φ in conjunction with assessment of the associated operating current has proved to be a useful characteristic variable for detecting short-term changes in behavior also in checking the operating condition (in condition monitoring).
Load feeders also have to be protected against overloading and short-circuits. Overload protection can be ensured by way of electronically simulating motor heating (motor model) using the time characteristic curve of the motor current. What, conversely, is required for the one “electronic” short-circuit protection is extremely fast threshold monitoring of the motor current (required reaction time=10 μs).
For acquisition and evaluation of the necessary measured values needed within the process of optimizing the consumption values of an installation, checking the operating condition, and protecting against overload and short-circuits, what have hitherto been required in a load feeder, particularly a three-phase load feeder, are expensive electronic circuits (analog technology+digital technology) consisting of a multiplicity of components.